SCH3U
Significant Digits Rules
ONLY USED FOR MEASURED VALUES i.e. mass, distance

The following digits are considered significant:

Any number from 1-9
Ex.
623 has 3 significant digits

Any zero between 2 significant digits
Ex.
603 has 3 significant digits

Any zero after a decimal point that also has significant digits before
the decimal point
Ex.
623.0 has 4 significant digits
The following zeros are not significant:

Leading zeros -any zero before a decimal point and other significant
digits are NOT SIGNIFICANT
Ex.
0.623
0.00623
0.0623000 (the last 3 zeros are significant)


Trailing zeros are usually significant
Sometimes trailing zeros are not significant
Ex.
When you want to record only 3 significant digits for a
number like 62311 you would write down 62300

Writing number in scientific notation makes it clear whether the
trailing zeros are significant:
Ex. 6.23 x 104 (3 sign. digits)
Or 6.230 x 104 (4 sign. digits)
Or 6.2300 x 104 (5 sign. digits)
Rules Used for Multiplying and Dividing

The final answer has the same number of significant digits as the
least number of significant digits in the question
Ex.
2/6 = 0.3333….. would be written 0.3
2.1/6.3 = 0.33
2.00/6.0 = 0.33
52 x 16 = 832 would be written 8.3 x 102 or 830
Rules for Adding and Subtracting



Ignore the number of significant digits
Consider the number of place values after the decimal
The final answer has the same number of decimal places as the least
number of decimal places in the question
Ex.
10.21
+ 20.0
30.21 BUT you would record no decimal places therefore the
correct answer would be 30.2